| Summary: | 碩士 === 國立中興大學 === 食品科學系 === 91 === Abstract
The Nisin-Controlled Expression system (NICE system) is an efficient gene expression system, and it was based on the mechanism of the autoregulation and biosynthesis of nisin in the Lactococcus lactis strains. The NICE system have been developed consisting of three essential elements: (1) nisin or nisin analogs or nisin mutants as inducer molecule; (2) a Gram-positive strain that expresses the nisRK genes to a desired level; and (3) plasmids containing the nisA or nisF promoter fragments, followed by convenient cloning sites to introduce the gene(s) of interest. The Model of NICE system is that the sensor protein NisK senses the presence of nisin as inducing signals, the phosphate group is transferred to response regulator NisR, which acts activate nisA promoter to expresses the gene(s). The main host of NICE system is Lactococcus lactis strains, other Gram-positive strains also can be used as the hosts. The gusA was used as the reporter gene, and the Lactobacillus paracasei was used as the dual plasmid NICE system host in this study.
The results indicate that the regulatory plasmid pNZ9530 and the expressive plasmid pNZ8008 can not be stable harbored in Lb. paracase host, the host might have unknow modification mechanism to the plasmids.
The study is also confirmed that nisin induction of the nisA promoter is extremely controlled by NisK and NisR proteins. Galactose also can be used as the inducer. When galactose is present, the downstream gene(s) transcripted from nisA promoter can express, but it seems still needs NisK and NisR as regulators. Higher concentrations of nisin under the cell tolerance level increase the induced expression from nisA promoter, but the optimal growth seems unfavorable for nisin induction. The extremely and flexible regulatory control is one of the main advantages of the NICE system.
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